Amnesty International, International Action Network on Small Arms and Oxfam International have joined forces for the countdown to the UN conference on small arms in June by launching the 100 Days campaign.
The coalition aims to galvanise supporters into pressurising governments to reach an international arms trade treaty at the conference in New York.
The three charities believe such a treaty would create legally binding arms controls that would ensure the sale of small arms met the same international standards across the world, and such controls would help to stop weapons falling into the hands of indiscriminate killers.
"The idea behind 100 Days is that it matches one of our key statistics," says James Dyson, campaign spokesman for Amnesty. "About 100,000 people will be killed or seriously injured by armed violence during those 100 days."
The campaign aims to put maximum pressure on governments to sign up to the treaty with 100 days of events designed to attract media coverage.
It was launched with a series of press conferences, rallies and stunts around the world. In the UK, campaigners submerged themselves in a bath of fake blood near the Houses of Parliament to mark the start of the campaign.
Well-known figures such as Archbishop Desmond Tutu and actress Helen Mirren signed an open letter to the media calling on governments to support the treaty. The countdown will culminate in a week of action from 22 May.
Meanwhile, supporters are able to keep up with events through the website, www.control arms.org. They can also join bands such as Editors and Scissor Sisters by adding their photographs to the Million Faces photo-petition, which is believed to be the largest of its kind. Supporters are encouraged to ask family and friends to do the same with e-cards that are available on the site.
"If 100 Days is successful, we will achieve the first comprehensive arms treaty," says Dyson. "There are already such treaties for biological, chemical and nuclear weapons, but nothing governing arms."